Non-technical abstractThis research program is focused on understanding and enlarging the class of materials in which atoms from the bottom rows of the periodic table play an important role. Crystalline compounds containing these elements have an interrelated set of properties including strong coupling between electron motion and spin, unusual magnetic behavior, broader electronic energy bands, and a tendency to pairwise attraction of neighboring atoms. Special attention is given to the exploration of layered materials that include tellurium, as these show a wide variety of structural motifs. First-principles computational methods are used to investigate candidate materials of this class, identifying those that appear most promising as targets for directed synthesis and in-depth experimental study. Comparisons between theory and experiment provide feedback to refocus the theoretical and computational effort. The team provides capabilities in bulk and thin-film materials growth coupled to characterization using optical, scattering, and scanning-probe techniques. The activity provides educational opportunities through the involvement of undergraduates in research, the coordination with outreach programs at the Liberty Science Center in New Jersey, and the organization of topical workshops and conferences.Technical AbstractInterest in 5d materials and 3d/5d hybrids has blossomed in recent years in response to scientific advances and applications in the areas of hard magnets, topological insulators, multiferroics, superconductors, and thermoelectrics. These materials are unique for several reasons. First, strong spin-orbit coupling competes with magnetic, crystal-field, many-body Coulomb, and other interactions in such a way as to drive new physical behaviors, such as the effective spin 1/2 state that emerges in certain iridates. Second, the bonding interactions associated with the larger size of the 5d orbitals promotes inter-cation dimerization in pairwise, chain-like, and other complex orderings. Third, the relativistic shifts in orbital energies, combined with spin-orbit coupling and bandwidth effects, can drive band inversions leading to topological phases and enhanced Rashba splittings. In 3d/5d hybrid materials, the interplay of these properties with the strong magnetic moments and correlation effects associate with the3d ions provides greater chemical flexibility and functional richness. The goal of the present project is to improve the understanding of how spin-orbit coupling enhances functionality in compounds containing 3d and 5d ions, and clarify how properties depend on control parameters such as spin-orbit strength, d-shell filling, dimensionality, and structural distortions. Specifically, the activity consists of a concerted theoretical and experimental exploration of materials in which 3d and 5d transition-metal sites coexist in multicomponent chalcogenide and oxide crystals and films. The unique physical and chemical properties of these materials provide a platform for a materials discovery paradigm in which first-principles computational methods are used to investigate candidate materials, identifying those that appear most promising as targets for directed synthesis and in-depth experimental study. Target materials systems include under-explored binary 5d tellurides, ternary 3d-5d tellurides and selenides, 3d-5d chalcogenide superlattices, and 3d-5d hexagonal chain compounds. The research also targets the synthesis of new materials and nanostructures for topological states including quantum anomalous Hall, strong topological insulator, and Weyl semimetal phases.The methods used in the research are diverse. Comparison between theory and experiment provides feedback to refocus the theoretical and computational effort, which is carried out using first-principles methods including density-functional theory and dynamical mean-field theory. The team provides capabilities in both bulk and thin-film (molecular beam epitaxy and pulsed-laser deposition) growth, while the understanding and optimization of the unique materials properties is facilitated using X-ray, optical, scanning tunneling, transport, and neutron scattering techniques.
|Effective start/end date||9/1/16 → 8/31/20|
- National Science Foundation (National Science Foundation (NSF))